This blog is a follow-up to a previous blog on medical testing. Here I will discuss the philosophy that underlies most, but not all medical testing. As you will learn, many tests have no clinical evidence of their usefulness, but that may not stop a doctor from ordering it or a patient from requesting it.
Firstly, I never worry about whether or not a test is "cost-efficient". My moral commitment is to my patient, and not to the amount of money his/her medical care may cost. That is not my decision to make. In other words, I am making a medical decision for one person and not for the 300,000,000 people who dwell within our borders, and I am sure you would want your personal doctor to think and act in the same manner.
Secondly, even if I think a test is not needed, and am fairly certain that the test will be negative, if the patient wants it I generally order it. To me, the fact that the patient will be relieved when the test comes back negative is generally sufficient reason to order it. Often the test is requested because a spouse suggested it, or a best friend came down with a particular disease, or it was discussed on TV or read about on the internet. For instance, for a while the magnesium content of red blood cells was thought to be related to chronic fatigue syndrome, so patients wanted this measured. I do, however, refuse to do tests suggested by The National Enquirer.
As I have mentioned in a previous blog, if a patient comes in requesting an HIV/AIDS test because he/she is starting a new sexual encounter, I refer them to the Red Cross or their nearest hospital. I explain that not only will the blood bank test the blood for AIDS for free (as well as for hepatitis and a host of other blood-borne diseases) but that they will also be helping their fellow citizens by their donation of a unit of blood. I also suggest that their future partner do the same.
Although there is absolutely no evidence that a vaginal ultrasound or the blood test CA-125 can detect ovarian cancer early enough to save lives, I will never deny a woman's request for these tests, because a negative test sharply reduces their worry/concern about having this dread disease.
I have a moral antipathy to the traveling ultrasound trucks that pull up to a nursing home and offer to test the residents for narrowing of their carotid or femoral arteries or an abdominal aortic aneurysm They tell the residents that they are giving them a half-price special because Medicare does not pay for these screening tests. But then they give the results to the patient and tell them to consult with their personal doctor about any abnormal results. To me, this is equivalent to abandoning the patient, and should be outlawed. Any doctor who orders or performs a test on a patient is morally (and should be legally) required to do all the necessary clinical follow-up of any abnormal results.
The same holds true for the total body CT scan that looks for calcium in your brain, your lungs, your coronary arteries and your abdomen. Again the patients are offered a "discount" and are told to follow-up with either their personal physician, or a physician at the hospital where the CT was done. The patient is never informed about the percentage of false positive tests, or if detecting calcium in a particular organ does indeed lead to an intervention that saves lives.
No comment is necessary about the PSA blood test for putative prostate cancer.
Patients should be made aware that the "normal" range for a given blood test is usually the average value of same sex adults plus or minus two standard deviations. This means, assuming the values of the blood tests are scattered "normally" (i.e. in a Gaussian distribution) throughout the test population, then for almost any blood test 5% of those tested will have an "abnormal" lab test, i.e. a value outside the "normal" range WITHOUT having a medical disease.
It is trivial to show that it then follows that in a panel of 25 blood tests, the average patient has a 50% chance (one out of two patients) of having an abnormal blood test. I have not even mentioned that there are racial differences in blood tests as well. For instance, without any disease, the average white blood cell count of white American adult women is 4.5, while the average white blood cell count of black American adult women is 3.5, just as the normal hemoglobin count for adult women is lower than that for adult men, and the normal ESR (sedimentation rate) is higher for women than for men, and teenagers have a "higher than normal" alkaline phosphatase because their bones are still growing. To repeat: you can have an "abnormal" blood test without having any illness at all, much in the same way that any plain Xray of the neck or lumbar spine of every adult 40 years old or older will always show "arthritis", even when the patient is pain-free.
The public is also blissfully unaware that the cutoff value for certain blood tests is determined (and not unanimously) by a group of doctors in Washington, D.C. much as one year the American Psychiatric Association voted that homosexuality should no longer be considered as evidence of a mental disease.
When I was in medical school, the upper value of "normal" fasting glucose was set at 140. It has since been lowered to 120, then 110, and most recently 100, with patients between the "normal" level and a glucose of 200 have been labeled "pre-diabetic". This label has increased their life insurance and long-term care insurance premiums without any demonstrated improvement in their health.
I will close by mentioning that not all clinical laboratories are equally skilled in measuring all lab tests (e.g. N-terminal parathormone), that some "normal" values for the same test are different for different labs, and that the first thing that should almost always be done with any abnormal blood test is to repeat it, rather than to automatically assume that the patient is ill.